Isolation, characterization and substrate-transport studies of a new, unique methylotroph
Keuer, Thomas Alan
Papoutsakis, E. Terry
Master of Science
Methylotrophic bacteria which assimilate carbon via the Ribulose Monophosphate Pathway are bioenergetically superior to other methylotrophs. The dehydrogenases which catalyze the oxidation of formaldehyde to formate and formate to CO2 in RMP bacteria produce much of the ATP required for biosynthesis. A strain, designated T15, has been isolated on the basis of high In vitro activities of the above two key enzymes, and has been biochemically characterized. The new strain exhibits high yields (up to .63 g cells/g MeOH) and growth rates (up to .46 hr) in batch culture? however, the yields and growth rates in continuous culture are significantly lower. Study of the transport mechanisms has provided valuable insight into the relationship between substrate uptake and the growth characteristics of T15. Experiments with radio-labelled substrates have indicated that methanol enters the cells primarily by diffusion? consequently, the bacteria are not able to accumulate methanol internally in order to support efficient continuous growth. Formaldehyde, on the other hand, is accumulated by an active transport system which depends on the A pH component of the membrane proton-motive force. The formate uptake mechanism is also dependent on the ApH, but ‘is more complex, possibly due to the uncoupling effect of the organic acid on the cell membrane.